HIRE AN EDITOR!!!
If you are not going to publish – fine. If you are writing for your own enjoyment or to send to a few friends. Fine. Edit as best you can. However, if you are planning on sending this out to more than a few family members and forgiving friends, you must hire an outside editor.
You must hire an outside editor.
Once more. You must hire an editor.
When I first started planning to bring out my own books, rather than do traditional publishing, I read a lot of books and sites. There are many different approaches. One piece of advice that ran through every single book and online article was the advice to hire an outside editor. I think Guy Kawasaki put it best in his great book, APE. He had read and edited his book many times. Many friends had read it. Then he sent it to an editor. She found thousands of mistakes. It amazes me every time, but it is one certainty in this very uncertain world. If you do not send your work to an outside editor, you will embarrass yourself.
Once the editor has gone through it, you should go through at least two more read throughs and at least one read aloud.
It has made me much more forgiving when I see errors and much more amazed when I don’t.
When I bring out a book, it has been worked over with a fine toothed comb at least ten times. The first time I see the book, I generally still find a couple of errors.
Good luck.